Yes schools should be making rules about appropriate attire. The photo you show just proves why such rules are necessary.
Unlike Alexandra Kerry's, Gabi's dress was perfectly appropriate.
Public schools, given we have them (and this type of rhubarb is a reason no to), should not be allowed to enforce sectarian dress codes. If the Mormons want that, they should be required to set up their own schools!
Really? Tell me, what right do public (i.e. government) schools have to tell parents (i.e. taxpayers i.e. their BOSSES)how to dress their children? What right would a county bureaucrat have to knock on your door and tell you what to wear? It is the same thing. Parents will judge what is appropriate for their children and public schools have no right to say different.